The invention generally relates to a turbine blade through which cooling fluid flows.
A turbine blade, through which cooling fluid flows, has internal flow ducts, which are separated from one another by internal walls. The working fluid flows around the turbine blade. The turbine blade can be a gas turbine blade. The working fluid is then gas. The turbine blade is inclined relative to the approaching working fluid, so that a force component in the peripheral direction of the turbine occurs in the usual manner. The efflux direction of the working fluid is, therefore, essentially that direction along the turbine blade in which the working fluid flows around the latter.
The type mentioned is a turbine blade in the rear region of a turbine. In this location, the working fluid has already expanded and cooled to such an extent that only slightly cooled turbine blades are employed. Thus, only a small flow of cooling fluid through the turbine is provided. Because of the small flow, a meander structure of flow ducts for the cooling fluid does not function satisfactorily in the case of slightly cooled turbine blades. Because of the slow flow velocity of the cooling fluid, the latter would have an excessive cooling effect in the initial region of a meandering flow duct and would be too strongly heated in the final region, in consequence, the cooling effect would be inadequate in that region; in the case of the turbine blades mentioned, the flow velocity of the cooling fluid can also be too low with respect to the centrifugal forces occurring due to the rotation of the turbine.
The cooling fluid therefore only flows in a simple manner along the radial extent of the turbine blade. In the case of simple flowxe2x80x94i.e. in the case of flow ducts with practically no reversal locations relative to the radial direction of the cooling fluid flowxe2x80x94the problems mentioned above do not occur. For this purpose, turbine blades are known which have radial holes or straight radial ducts extending from a radially inner blade root to outlet flow openings located further radially outwardxe2x80x94outlet flow openings introduced into the rubbing edge. The resulting cooling fluid flow then has the desired localxe2x80x94at each location of the flow ductxe2x80x94radial flow components which are expediently directed, predominantly to exclusively, radially outward.
Because of the technically determined minimum dimensions of both the cast core and the wall thickness, the flow, and therefore also the cooling effect, is strongly inhomogeneous in such turbine blades. As an example, the region of a trailing edge, which has to become narrower in the efflux direction, can as a rule no longer have a radial flow duct passing through it because of the minimum dimensions mentioned, determined by the manufacturing process. The result is overheating of the overhanging trailing edge. In addition, there are limitationsxe2x80x94in particular due to the minimum dimensions mentioned abovexe2x80x94to the geometry of the usually large turbine blades in the rear region of the turbine.
An object of an embodiment of the present invention is to provide a turbine blade which, despite a small cooling fluid flow, is matched in terms of its geometry to the technical requirements for slightly cooled turbine blades and nevertheless permits substantially homogeneous cooling, in particular in the edge zones.
An embodiment of the invention offers the advantage that it permits a homogeneous cooling of the turbine blade, in particular in the region of the edges. The region of the trailing edge duct, in which the aerodynamic requirements demand narrowing of the turbine blade, for example, is particularly problematic in this connection.
The advantage mentioned may be achieved by one or more trailing edge ducts being present whose cooling fluid flow have local transverse flow components at predetermined locations, outlet flow openings being introduced into a trailing edge of the turbine blade for these trailing edge ducts. The use of the trailing edge as the region for the outlet flow of the cooling fluid opens a large variety of design possibilities, which were not previously accessible, for slightly cooled turbine blades.
As an example, the trailing edge ducts canxe2x80x94at least in partxe2x80x94conduct their cooling fluid away via the outlet flow openings which are introduced into the trailing edge. By this, more free space is also created for the ducts locatedxe2x80x94viewed in the efflux directionxe2x80x94before the trailing edge ducts. Outlet flow openings, particularly on the rubbing edge, admission to which had previously been through the trailing edge ducts, can now be used for conducting away cooling fluid from flow ducts located in front of the trailing edge ducts.
A trebly useful effect is achieved: by this it is, namely, possible for the first time to effectively and homogeneously cool the trailing edge of a turbine blade according to an embodiment of the invention and to have, at the same time, a thin trailing edge (with respect to improved aerodynamics). In addition, a natural efflux of the cooling fluid is achieved for the trailing edge ducts and this also permits the front flow ducts located in front of the trailing edge ducts to be matched, in their geometry and particularly in their efflux behavior, to the technical requirements.
Thus, for example, front flow ducts can provide admission to more outlet flow length along the rubbing edge than was previously the case. Because the trailing edge ducts are, on the one hand, displaced further in the efflux direction toward the trailing edge and, on the other, are deflected due to their bent shape, the front flow ducts located in front of them can fill the resulting free space. Due to the local transverse flow components of the trailing edge ducts, the front flow ducts can likewise be bent in such a way that they also have local transverse flow components. This provides a different space utilization within the cooling volume of the turbine blade, with better utilization of the cooling air.
By this, even turbine blades in the rear region of the turbinexe2x80x94i.e. turbine blades with little coolingxe2x80x94can, for the first time, be embodied with minimum to disappearing limitations with respect to the geometry. It is, for example, an adequately known requirement (for strength reasons and casting reasons) that the turbine blade should become narrower away from the blade root in the radial direction. Because the outlet flow openings of the trailing edge are used, the other flow ducts, in particular the front and central flow ducts, can be extended in this direction in terms of their extent parallel to the efflux direction and, therefore, can compensate for the decrease in thickness in the radial direction by spreading parallel to the efflux direction and utilizing a plurality of the outlet flow openings in the rubbing edge by use of a flow duct. By this, a practically constant internal cross section of the flow ducts can be achieved, at the best possible efficiency of the turbine, in association with a slender profile. This is only possible by use of an embodiment of the invention because the additional space is only made possible by the outlet flow openings now freed on the rubbing edge and by the curved shape of the flow ducts. In addition, a profile shape imposed to optimize the aerodynamics (edge zone effect) is possiblexe2x80x94in contrast to drilled bladesxe2x80x94with a cooling possibility for the trailing edge, in contrast to previous geometries.
The flow ducts can be shaped in such a way that transverse flow components are present in the efflux direction and opposite to it. Exclusively or predominantly transverse flow components in the efflux direction are, however, preferred. The transverse flow components effect a flow through the trailing edge, which was not previously present. Due to the utilization of the transverse flow components mentioned, furthermore, the cooling fluid is automatically conducted to the outlet flow openings in the trailing edge.
Preference is given to a trailing edge duct and/or a front flow duct which deflect/deflects, at least in sections, from the radial direction in the efflux direction, in particular with their/its outer radial sections.
In order to avoid dead zones and to reduce the flow resistance overall, so that the total cooling volume available is effectively utilized, provision is made for the deflection sections to be rounded. The deflection sections then extend without edges and with curvature.
A plurality of trailing edge ducts can be present. In particular, the last trailing edge duct, viewed in the efflux direction, is provided practically exclusively with outlet flow openings introduced into the trailing edge. On the basis of the inventive idea of utilizing transverse flow components and providing outlet flow openings in the trailing edge, this is the most effective solution and as few outlet flow openings as possiblexe2x80x94preferably no outlet flow openings at allxe2x80x94other than those of the trailing edge have fluid admitted to them and are, in consequence, occupied.
The last trailing edge duct can, therefore, also end before the rubbing edge radially inward at a radial distance. According to an embodiment of the invention, this duct needs, namely, no outlet flow openings in the rubbing edge at all. This first permits a particularly effective shaping of the turbine bladexe2x80x94in particular with respect to the efficiency of the turbine.
In addition, a radially continuous trailing edge duct can be present which has both outlet flow openings which are introduced into the rubbing edge and outlet flow openings which are introduced into the trailing edge. Such a radially continuous trailing edge duct forms, more or less, the transition between a front flow duct and a trailing edge duct, which only has outlet flow openings which are introduced into the trailing edge. A gentle transition is achieved by use of such a radially continuous trailing edge duct. The cooling volume available can be effectively utilized by this.
It is then, for example, possible for the last trailing edge duct to have outlet flow openings which are located further radially inward and are introduced into the trailing edge and for the radially continuous trailing edge duct to have outlet flow openings which are located radially further outward and are introduced into the trailing edge. An opening, that is a penetration in the internal region between the two flow ducts, can be provided between the last trailing edge duct and the radially continuous trailing edge duct. The wall between the individual flow ducts, which separates all flow ducts, is then interrupted at the location of the opening. The continuous connection is used to permit casting capability with respect to the core position.
As already stated above, an embodiment of the invention achieves the effect that the local, resultant, effective internal cross section is practically of the same size over the complete length of a flow duct with the exception of negligible cross-sectional deviations relating to the flow resistance of the flow duct. The cross-sectional deviations are preferably less than 20 percent and, in particular, less than 10 percent, of the internal cross section mentioned. The resultant, effective overall cross-sectional area of the inlet flow openings is preferably equal to the overall cross-sectional area of the outlet flow openings of a flow duct, the respective overall cross-sectional area corresponding to the internal cross section of the associated flow duct.
A turbine blade according to an embodiment of the invention has little cooling, i.e. is embodied without the meander structure of the flow ducts. It is used for the rear region of a turbine and/or for turbines/turbine blades with little cooling.